public LfsRecord ReadRecord(ulong lsn)
{
if (m_restartPage == null)
{
m_restartPage = ReadRestartPage();
}
ulong pageOffsetInFile = LsnToPageOffsetInFile(lsn);
int recordOffsetInPage = LsnToRecordOffsetInPage(lsn);
LfsRecordPage page = ReadPage(pageOffsetInFile);
if (page == null)
{
throw new InvalidDataException("LfsRecord LSN points to an uninitialized page");
}
int dataOffset = m_restartPage.RestartArea.LogPageDataOffset;
LfsRecord record = page.ReadRecord(recordOffsetInPage);
if (record.ThisLsn != lsn)
{
throw new InvalidDataException("LfsRecord LSN does not match expected value");
}
if (record.Length < LfsRecord.HeaderLength)
{
throw new InvalidDataException("LfsRecord length is invalid");
}
if (record.IsMultiPageRecord)
{
int recordLength = (int)(LfsRecord.HeaderLength + record.ClientDataLength);
int bytesRemaining = recordLength - (LfsRecord.HeaderLength + record.Data.Length);
while (bytesRemaining > 0)
{
pageOffsetInFile += m_restartPage.LogPageSize;
if (pageOffsetInFile == m_restartPage.RestartArea.FileSize)
{
pageOffsetInFile = m_restartPage.SystemPageSize * 2 + m_restartPage.LogPageSize * 2;
}
page = ReadPage(pageOffsetInFile);
int bytesToRead = Math.Min((int)m_restartPage.LogPageSize - dataOffset, bytesRemaining);
record.Data = ByteUtils.Concatenate(record.Data, page.ReadBytes(dataOffset, bytesToRead));
bytesRemaining -= bytesToRead;
}
}
return(record);
}
/// <summary>
/// This method will repair the log file by copying the tail copies back to their correct location.
/// If necessary, the restart area will be updated to reflect CurrentLsn and LastLsnDataLength.
/// </summary>
/// <remarks>This method will only repair the log file, further actions are needed to bring the volume back to a consistent state.</remarks>
private void RepairLogFile()
{
if (m_restartPage == null)
{
m_restartPage = ReadRestartPage();
}
// Note: this implementation is not as exhaustive as it should be.
LfsRecordPage firstTailPage = null;
LfsRecordPage secondTailPage = null;
try
{
firstTailPage = ReadPageFromFile(m_restartPage.SystemPageSize * 2);
}
catch (InvalidDataException)
{
}
try
{
secondTailPage = ReadPageFromFile(m_restartPage.SystemPageSize * 2 + m_restartPage.LogPageSize);
}
catch (InvalidDataException)
{
}
// Find the most recent tail copy
LfsRecordPage tailPage = null;
if (firstTailPage != null)
{
tailPage = firstTailPage;
}
if (tailPage == null || (secondTailPage != null && secondTailPage.LastEndLsn > firstTailPage.LastEndLsn))
{
tailPage = secondTailPage;
}
if (tailPage != null)
{
LfsRecordPage page = null;
try
{
page = ReadPageFromFile(tailPage.LastLsnOrFileOffset);
}
catch (InvalidDataException)
{
}
if (page == null || tailPage.LastEndLsn > page.LastLsnOrFileOffset)
{
ulong pageOffsetInFile = tailPage.LastLsnOrFileOffset;
tailPage.LastLsnOrFileOffset = tailPage.LastEndLsn;
WritePage(pageOffsetInFile, tailPage);
if (tailPage.LastEndLsn > m_restartPage.LogRestartArea.CurrentLsn)
{
m_restartPage.LogRestartArea.CurrentLsn = tailPage.LastEndLsn;
int recordOffsetInPage = LsnToRecordOffsetInPage(tailPage.LastEndLsn);
LfsRecord record = tailPage.ReadRecord(recordOffsetInPage);
m_restartPage.LogRestartArea.LastLsnDataLength = (uint)record.Data.Length;
WriteRestartPage(m_restartPage);
}
}
}
}